Pixel designs of improving the aperture ratio in an LCD

ABSTRACT

This invention in one aspect relates to a pixel structure. In one embodiment, the pixel structure includes a scan line formed on a substrate and a data line formed over the substrate defining a pixel area, a switch formed inside the pixel area on the substrate, a shielding electrode having a first portion and a second portion extending from the first portion, and formed over the scan line, the data line and the switch, where the first portion is overlapped with the switch and the second portion is overlapped with the data line, and a pixel electrode having a first portion and a second portion extending from the first portion, and formed over the shielding electrode in the pixel area, where the first portion is overlapped with the first portion of the shielding electrode so as to define a storage capacitor therebetween and the second portion has no overlapping with the second portion of the shielding electrode.

FIELD OF THE INVENTION

The present invention relates generally to a liquid crystal display(LCD), and more particularly, to an LCD that utilizes a pixel design toimprove the aperture ratio thereof and methods of fabricating same.

BACKGROUND OF THE INVENTION

A liquid crystal display (LCD) device includes an LCD panel formed withliquid crystal cells and pixel structures with each associating with acorresponding liquid crystal cell and having a scan line, a data line, apixel electrode, and a switch having a gate, a source and a drainelectrically connected to the scan line, the data line and the pixelelectrode, respectively. Generally, an aperture ratio of pixels directlyaffects utilization of backlight and panel brightness of an LCD. In apixel structure, a capacitance, C_(pd), between the pixel electrode andthe data line is one of major factors affecting the aperture ratio. Thecapacitance C_(pd) is determined by the distance between the pixelelectrode and the data line. The closer the pixel electrode and the dataline are, the larger the capacitance C_(pd) is. However, when the pixelelectrode and the data line are too close, a cross talk may be generatedby the coupling effect between the charged potential on the pixelelectrode and the signal voltages transmitted in the data line, whichdeteriorates the display quality of the LCD. Generally, the data line isalways designed to be separated from the pixel electrode for a distanceso as to avoid the cross talk. However, the longer the distance betweenthe data line and the pixel electrode is, the more greatly the apertureratio of the pixel decreases.

To reduce the cross talk of the pixel structure and maintain theaperture ratio of the pixel structure at a certain level, variousdesigns of pixel structures have been developed. For example, one of thepixel designs is the utilization of a shielding electrode disposedbetween the pixel electrode and the data line to reduce the effect ofcapacitance C_(pd). As shown in FIG. 6, in the pixel design, theshielding electrode 640 is formed over the date line 620 and the switch650, but under the pixel electrode 610, such that the shieldingelectrode 640 has an area 660 that is overlapped with the peripheralportion of the pixel electrode 610. For such a pixel design, theoverlapped area 660 of the shielding electrode 640 with the peripheralportion of the pixel electrode 610 is configured to generate a storagecapacitance therebetween, thereby improving the aperture ratio thereof,in comparison with a pixel design without a shielding electrode.However, the shielding electrode 640 is usually formed of an opaqueconductive material because of impedance. Thus, the use of theoverlapped area 660 of the shielding electrode 640 with the peripheralportion of the pixel electrode 610 to generate the storage capacitanceitself reduces certain amounts of the aperture ratio.

Additionally, some pixel designs also utilize a comb-like pixelelectrode 710 to assist with the orientations of liquid crystals, asshown in FIG. 7. In the pixel design 700, the storage capacitance area760 formed by overlapping the shielding electrode 740 with theperipheral portion of the pixel electrode 710 is reduced because of thecomb-like structure of the pixel electrode 710. Increasing the storagecapacitance area, thereby increasing the storage capacitance, willreduce the aperture ratio.

Therefore, a heretofore unaddressed need exists in the art to addressthe aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

The present invention, in one aspect, relates to a pixel structureusable in a liquid crystal display (LCD). In one embodiment, the pixelstructure has a scan line formed on a substrate and a data line formedover the substrate, and a pixel area associated with the data line andthe scan line. The pixel structure also has a switch formed inside thepixel area on the substrate.

Furthermore, the pixel structure has a shielding electrode having afirst portion and a second portion extending from the first portion, andformed over the scan line, the data line and the switch, where the firstportion is overlapped with the switch and the second portion isoverlapped with the data line. The second portion of the shieldingelectrode is configured to shield the electric field produced from thedata line. In one embodiment, the shielding electrode is made of anopaque, conductive material.

Additionally, the pixel structure has a pixel electrode having a firstportion and a second portion extending from the first portion, andformed over the shielding electrode in the pixel area. The first portionis overlapped with the first portion of the shielding electrode so as todefine a storage capacitor therebetween. The second portion has nooverlapping with the second portion of the shielding electrode. In oneembodiment, the pixel electrode has a comb-like shape. The pixelelectrode is made of a transparent, conductive material.

The pixel structure also has a first insulation layer formed between thescan line and the data line, a second insulation layer formed betweenthe data line and the shielding electrode; and a third insulation layerformed between the shielding electrode and the pixel electrode.

The switch has a gate, a source and a drain electrically connected tothe scan line, the data line and the pixel electrode, respectively. Thegate of the switch is formed on the substrate, and the source and drainof the switch are formed between the first insulation layer and thesecond insulation layer.

In one embodiment, the switch further includes a semiconductor layerformed between the source and drain and the first insulation layer. Thesemiconductor layer includes a channel layer formed on the firstinsulation layer and an ohmic contact layer formed on the channel layer.In one embodiment, the channel layer a formed of amorphous silicon(a-Si), and the ohmic contact layer is formed of an N⁺ doped or CVDdeposited semiconductor. The switch is corresponding to a thin filmtransistor (TFT).

In another aspect, the present invention relates to a liquid crystaldisplay (LCD) comprising a plurality of the pixel structures, arrangedin a matrix.

In yet another aspect, the present invention relates to method forfabricating a pixel structure. In one embodiment, the method includesthe following steps: at first, a substrate is provided. A scan line anda gate electrode are formed on the substrate. The gate electrode isformed to be electrically connected to the scan line. Then, a firstinsulation layer is formed on the substrate, which overlays the scanline and the gate electrode.

Then, a semiconductor layer is formed on the first insulation layer andoverlapped with the gate electrode. In one embodiment, the step offorming the semiconductor layer may comprises the steps of forming achannel layer on the first insulation layer, forming an ohmic contactlayer on the channel layer, and patterning the channel layer and theohmic contact layer to form the semiconductor layer, where the ohmiccontact layer is patterned to have a first portion and a second portionseparated from the first portion. Next, a data line is formed on thefirst insulation layer. Meanwhile, a source electrode and a drainelectrode are formed on the first portion and the second portion of theohmic contact layer, respectively. In alternative steps, after formingthe channel layer and the ohmic contact layer, a step of pre-patterningthe channel layer and the ohmic contact layer can be performed to definethe shape of the channel layer. A step of patterning the channel layerand the ohmic contact layer can be performed after forming the sourceelectrode and the drain electrode, wherein the ohmic contact layer ispatterned to have a first portion and a second portion separated fromthe first portion, and the source electrode and the drain electrode aresubstantially in contact with the first portion and the second portionof the ohmic contact layer, respectively. In further alternative steps,a half-tone process is employed, the step of patterning the channellayer and the ohmic contact layer can be performed after forming thesource electrode and the drain electrode with a half-tone mask, whereinthe ohmic contact layer is patterned to have a first portion and asecond portion separated from the first portion, and the sourceelectrode and the drain electrode are substantially in contact with thefirst portion and the second portion of the ohmic contact layer,respectively. The gate electrode, the channel layer, the ohmic contactlayer, the source electrode and the drain electrode define a switch.

The next step is to form a second insulation layer on the firstinsulation layer, which overlays the data line and the switch. Ashielding electrode is formed on the second insulation layer. Theshielding electrode has a first portion overlapped with the switch, anda second portion extending from the first portion and overlapped withthe data line.

Next, a third insulation layer is formed on the second insulation layer,which overlays the shielding electrode. Then, a pixel electrode isformed on the third insulation layer. The pixel electrode has a firstportion overlapped with the first portion of the shielding electrode soas to define a storage capacitor therebetween, and a second portionextending from the first portion having no overlapping with the secondportion of the shielding electrode.

The source electrode and the drain electrode of the switch areelectrically connected to the data line and the pixel electrode,respectively.

The channel layer a formed of amorphous silicon (a-Si), and wherein theohmic contact layer is formed of an N⁺ doped or CVD depositedsemiconductor.

In one embodiment, the shielding electrode comprises an opaque,conductive material.

The pixel electrode has a comb-like shape. The pixel electrode is madeof a transparent, conductive material.

These and other aspects of the present invention will become apparentfrom the following description of the preferred embodiment taken inconjunction with the following drawings, although variations andmodifications therein may be affected without departing from the spiritand scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate one or more embodiments of theinvention and, together with the written description, serve to explainthe principles of the invention. Wherever possible, the same referencenumbers are used throughout the drawings to refer to the same or likeelements of an embodiment, wherein:

FIGS. 1 a-1 c show schematically a pixel structure according to oneembodiment of the present invention, (a) a top view, (b) a top view withhighlighting a storage capacitance, and (c) a cross-sectional view;

FIG. 2 shows partially a pixel design including 4 pixels according toanother embodiment of the present invention;

FIG. 3 shows partially a pixel design including 4 pixels according toanother embodiment of the present invention;

FIG. 4 shows schematically a pixel structure according to anotherembodiment of the present invention, (a) a top view, and (b) a top viewwith highlighting a storage capacitance;

FIGS. 5 a-5 h show schematically cross-sectional views illustrating amethod for fabricating a pixel structure according to one embodiment ofthe present invention;

FIG. 6 shows schematically a conventional pixel structure, (a) a topview, and (b) a top view with highlighting a storage capacitance; and

FIG. 7 shows schematically another conventional pixel structure, (a) atop view, and (b) a top view with highlighting a storage capacitance.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is more particularly described in the followingexamples that are intended as illustrative only since numerousmodifications and variations therein will be apparent to those skilledin the art. Various embodiments of the invention are now described indetail. Referring to the drawings, like numbers indicate like componentsthroughout the views. As used in the description herein and throughoutthe claims that follow, the meaning of “a”, “an”, and “the” includesplural reference unless the context clearly dictates otherwise. Also, asused in the description herein and throughout the claims that follow,the meaning of “in” includes “in” and “on” unless the context clearlydictates otherwise. Without intent to limit the scope of the invention,exemplary apparatuses and methods and their related results according tothe embodiments of the present invention are given below.

The description will be made as to the embodiments of the presentinvention in conjunction with the accompanying drawings in FIGS. 1-5. Inaccordance with the purposes of this invention, as embodied and broadlydescribed herein, this invention, in one aspect, relates to a pixelstructure, and a liquid crystal display (LCD) comprising a plurality ofthe pixel structures, arranged in a matrix.

Referring to FIGS. 1 a-1 c, the pixel structure 100 has a scan line 110and a data line 120, a pixel area 105 defined between the data line 120and the data line 122 of its adjacent pixel structure (not shown), aswitch 150, a shielding electrode 130 and a pixel electrode 140. Theswitch 150 and the pixel electrode 140 are formed inside the pixel area105. The pixel structure 100 further has a first insulation layer 172,the second insulation layer 174 and the third insulation layer 176. Theswitch 150 has a gate electrode 151, a source electrode 155 and a drainelectrode 156 electrically connected to the scan line 110, the data line120 and the pixel electrode 140, respectively. Additionally, the switch150 also includes a channel layer 152, an ohmic contact layer 153/154formed between the gate electrode 151 and the source electrode 155 andthe drain electrode 156. In one embodiment, the channel layer 152 isformed of amorphous silicon (a-Si), and the ohmic contact layer 153/154is formed of an N⁺ doped or CVD deposited semiconductor. The switch 150is corresponding to a thin film transistor (TFT).

The gate electrode 151, the data line 120 and the scan line 110 arespatially formed on the substrate 101. The gate electrode 151 defines aswitch area therearound. The first insulation layer 172 is formed on thesubstrate 101 and overlays the scan line 110 and the gate electrode 151.The channel layer 152 is formed on the first insulation layer 172. Thechannel layer 152 layer is overlapped with the gate electrode 151. Theohmic contact layer 153/154 is formed on the channel layer 152. Theohmic contact layer 153/154 has a first portion 153 and a second portion154 separated from the first portion 153. The data line 120 and thesource electrode 155 and the drain electrode 156 are formedsimultaneously. The source electrode 155 and the drain electrode 156 areformed on the first portion 153 and the second portion 154 of the ohmiccontact layer 153/154, respectively.

The second insulation layer 174 is formed on the first insulation layer172 and overlays the data line 120 and the switch 150. The shieldingelectrode 130 is formed on the second insulation layer 174. Theshielding electrode 130 includes a first portion 132 that is overlappedwith the switch 150, and a second portion 134 that extends from thefirst portion 132 and is overlapped with the data line 120. The thirdinsulation layer 176 is formed on the second insulation layer 174 andoverlays the shielding electrode 130. Considering the impedance of thepixel, the shielding electrode 130 is usually made of an opaque,conductive material.

The pixel electrode 140 is formed on the third insulation layer 176. Thepixel electrode 140 includes a first portion 142 overlapped with thefirst portion 132 of the shielding electrode 130, and a second portion144 extending from the first portion 142. The pixel electrode 140 ismade of a transparent, conductive material, such as indium zinc oxide(IZO), amorphous indium tin oxide (ITO), poly ITO, or the like.

According to the present invention, the switch 150 is formed inside thepixel area 105. The first portion 132 of the shielding electrode 130 andthe first portion 142 of the pixel electrode 140 and the thirdinsulation layer 176 between the first portion 132 of the shieldingelectrode 130 and the first portion 142 of the pixel electrode 140 areconfigured as a storage capacitor 160 to generate a storage capacitance,i.e., the storage capacitance area 160 is defined by the area of theshielding electrode 130 and the pixel electrode 140 and the thirdinsulation layer 176 between the shielding electrode 130 and the pixelelectrode 140 located over the switch 150. Furthermore, the secondportion 144 of the pixel electrode 140 has no overlapping with thesecond portion 134 of the shielding electrode 130. As shown in FIGS. 1 aand 1 c, the second portion 144 of the pixel electrode 140 and thesecond portion 134 of the shielding electrode 130 are separated by agap, d≧0, and preferably, d≈0. Accordingly, the pixel area 105 can beoptimally utilized to transmit light therethrough the pixel electrode144, thereby increasing the aperture ratio of the pixel.

In this exemplary embodiment, the switch 150 is formed inside thecentral region of the pixel area 105. In practice, the switch 150 canalso be formed inside the other region of the pixel area 105.

FIG. 2 shows a pixel design 200 according to one embodiment of thepresent invention. In the exemplary pixel design 200, only four pixelstructures 205 a, 205 b, 205 c and 205 d are shown and arranged in amatrix. Each pixel structure 205 a, 205 b, 205 c or 205 d is essentiallysame as that shown in FIG. 1 a-1 c. The pixel electrodes 240 a and 240 bof each two neighboring pixel structures 205 a and 205 b along adirection of the data lines 220 are separated be a first space 280, andthe pixel electrodes 240 a and 240 c of each two neighboring pixelstructures 205 a and 205 c along a direction of the scan lines 210 areseparated be a second space 290. The data lines 220 are located in thesecond space 290. Further, the shielding electrodes 230 are formed inthe second space 290 and overlap with the data lines 220. As shown inFIG. 2, no portion of the shielding electrodes 230 is formed in thefirst space 280.

In practice, any number of the pixel structures can be utilized.

FIG. 3 shows a pixel design 300 according to another embodiment of thepresent invention. The pixel design 300 is similar to the pixel design200 shown in FIG. 2, excerpt that a portion of the shielding electrode330 is formed in the first space 380.

Referring to FIG. 4, a pixel structure 400 is shown according to anotherembodiment of the present invention. The pixel structure 400 is similarto the pixel structure 100 shown in FIGS. 1 a-1 c, excerpt that thepixel electrode 440 has a comb-like structure. Accordingly, for such apixel structure 400, the aperture ratio of the pixel can be improved.

FIGS. 5 a-5 h show a method of fabricating a pixel structure accordingto one embodiment of the present invention. The method includes thefollowing steps: at first, a substrate 501 is provided. The firstsubstrate 501 is formed of glass, plastic or the likes. Then, a scanline 510 and a gate electrode 551 are spatially formed on the substrate501. The gate electrode 551 is formed of a metal such as Al, Mo, Cr, Ta,or alloy, and electrically connected to the scan line 510.

A first insulation layer (gate insulation layer) 572 is formed on thesubstrate 501, and overlays the scan line 510 and the gate electrode551. The first insulation layer 572 is formed of SiNx, SiOx, or SiON.

Then, a semiconductor layer 559 is formed on the first insulation layer572. The semiconductor layer 559 includes a channel layer 552 formed onthe first insulation layer 572 and overlapped with the gate electrode551, and an ohmic contact layer 558 formed on the channel layer 552 andpatterned to have a first contact portion 553 and a second contactportion 554 separated from the first contact portion 553. The channellayer 552 can be formed of amorphous silicon (a-Si) or the like. Thecontact layer 558 can be formed of doped amorphous silicon such as N⁺doped a-Si. In one embodiment, the channel layer 552 and the contactlayer 558 are formed in such a manner that the a-Si and the dopedamorphous silicon (N⁻ doped a-Si or P⁺ doped a-Si) are successivelydeposited by PECVD and then patterned. Next, a data line 520 and asource electrode 555 and a drain electrode 556 are formed. The sourceelectrode 555 and the drain electrode 556 are formed on the firstportion 553 and the second portion 554 of the ohmic contact layer,respectively. In alternative steps, after forming the channel layer 552and the ohmic contact layer 558, a step of pre-patterning the channellayer 552 and the ohmic contact layer 558 can be performed to define theshape of the channel layer 552. A step of patterning the channel layer552 and the ohmic contact layer 558 can be performed after forming thesource electrode 555 and the drain electrode 556, wherein the ohmiccontact layer 558 is patterned to have a first contact portion 553 and asecond contact portion 554 separated from the first contact portion 553,and the source electrode 555 and the drain electrode 556 aresubstantially in contact with the first contact portion 553 and thesecond contact portion 554 of the ohmic contact layer 558, respectively.In further alternative steps, a half-tone process is employed, the stepof patterning the channel layer 552 and the ohmic contact layer 558 canbe performed after forming the source electrode 555 and the drainelectrode 556 with a half-tone mask, wherein the ohmic contact layer 558is patterned to have the first contact portion 553 and the secondportion 554 separated from the first contact portion 553, and the sourceelectrode 555 and the drain electrode 556 are substantially in contactwith the first contact portion 553 and the second contact portion 554 ofthe ohmic contact layer 558, respectively.

The source electrode 555 and the drain electrode 556 of the switch 550are electrically connected to the data line 520 and the pixel electrode540. The gate electrode 551, the gate insulation layer 572, the channellayer 552, the ohmic contact layer 558, the source electrode 555 and thedrain electrode 556 define a switch 550, which corresponds to a TFT.

Afterwards, a second insulation layer 574 is formed on the firstinsulation layer 572 and overlays the data line 520 and the switch 550.Then, a shielding electrode 530 is formed on the second insulation layer574. The shielding electrode 530 has a first portion 532 overlapped withthe switch 550, and a second portion 534 extending from the firstportion 532 and overlapped with the data line 520. The shieldingelectrode 530 is formed of an opaque, conductive material.

The next step is to form a third insulation layer 576 on the secondinsulation layer 574, which overlays the shielding electrode 530. Then,a pixel electrode 540 is formed on the third insulation layer 576. Thepixel electrode 540 has a first portion 542 and a second portion 544extending from the first portion 342. The first portion 542 of the pixelelectrode 540 is overlapped with the first portion 532 of the shieldingelectrode 530 so as to define a storage capacitor 560 with the thirdinsulation layer 576 therebetween. The second portion 544 of the pixelelectrode 540 is configured to have no overlapping area with the secondportion 534 of the shielding electrode 530. The pixel electrode 540 ismade of a transparent, conductive material.

In sum, the present invention, among other things, recites a pixelstructure having a switch, a shielding electrode, and a pixel electrodeformed inside the pixel area in a multilayered structure. The firstportion of the shielding electrode and the first portion of the pixelelectrode located over the switch and the third insulation layertherebetween are configured as a storage capacitor to generate a storagecapacitance. Furthermore, the second portion of the pixel electrode hasno overlapping with the second portion (located over the data line) ofthe shielding electrode. Accordingly, the pixel area can be optimallyutilized to transmit light therethrough the pixel electrode, therebyincreasing the aperture ratio of the pixel.

The foregoing description of the exemplary embodiments of the inventionhas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations are possiblein light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the invention and their practical application so as toactivate others skilled in the art to utilize the invention and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present inventionpertains without departing from its spirit and scope. Accordingly, thescope of the present invention is defined by the appended claims ratherthan the foregoing description and the exemplary embodiments describedtherein.

1. A pixel structure usable in a liquid crystal display (LCD),comprising: (a) a scan line formed on a substrate; (b) a data lineformed over the substrate; (c) a pixel area associated with the scanline and the data line; (d) a switch formed inside the pixel area on thesubstrate; (e) a shielding electrode having a first portion and a secondportion extending from the first portion, and formed over the scan line,the data line and the switch, wherein the first portion is overlappedwith the switch, and wherein the second portion is overlapped with thedata line wherein the first and second portions are formed adjacent andover the switch; and (f) a pixel electrode having a first portion and asecond portion extending from the first portion, and formed over theshielding electrode in the pixel area, wherein the first portion isoverlapped with the first portion of the shielding electrode so as todefine a storage capacitor therebetween, and wherein the second portionhas no overlapping with the second portion of the shielding electrode,wherein the switch has a gate, a source and a drain electricallyconnected to the scan line, the data line and the pixel electrode,respectively.
 2. The pixel structure of claim 1, further comprising: (a)a first insulation layer formed between the scan line and the data line;(b) a second insulation layer formed between the data line and theshielding electrode; and (c) a third insulation layer formed between theshielding electrode and the pixel electrode.
 3. The pixel structure ofclaim 2, wherein the gate of the switch is formed on the substrate, andthe source and drain of the switch are formed between the firstinsulation layer and the second insulation layer.
 4. The pixel structureof claim 3, wherein the switch further comprises a semiconductor layerformed between the source and drain and the first insulation layer. 5.The pixel structure of claim 4, wherein the semiconductor layercomprises a channel layer formed on the first insulation layer and anohmic contact layer formed on the channel layer.
 6. The pixel structureof claim 5, wherein the channel layer is formed of amorphous silicon(a-Si), and wherein the ohmic contact layer is formed of an N⁺ doped orCVD deposited semiconductor.
 7. The pixel structure of claim 1, whereinthe switch comprises a thin film transistor.
 8. The pixel structure ofclaim 1, wherein the second portion of the shielding electrode isconfigured to shield the electric field produced from the data line. 9.The pixel structure of claim 1, wherein the shielding electrode is madeof an opaque, conductive material.
 10. The pixel structure of claim 1,wherein the pixel electrode has a comb-like shape.
 11. The pixelstructure of claim 1, wherein the pixel electrode is made of atransparent, conductive material.
 12. A liquid crystal display (LCD)comprising a plurality of the pixel structures of claim 1, arranged in amatrix.